Ever since Spanish Patent ES 150519, for example, a counterweight sash window has been known, which window incorporates a mechanism comprising cables, pulleys and weights, intended to assist the vertical movement of the sashes. In the closed position, the window sashes are arranged one after the other, forming a single vertical plane; nevertheless both sashes are guided, the inner sash in lateral guides in the casing that drive its vertical and horizontal path to the outside, and the outer sash in lateral guides that drive it in its vertical path. The horizontal movement of the inner sash to the outside situates the sash in the same vertical plane as that occupied by the outer sash, thus permitting the setting and adjustment of the ruled surfaces of the bottom edge of the outer sash over the top edge of the inner sash. The invention describes the presence of joint covers and weather stripping that clearly do not guarantee the sealing of the window.
A counterweight vertical-movement mechanism that includes a counterbalanced spring for counterweighting suspended elements has been already disclosed in U.S. Pat. No. 1,922,370, which describes a rotatable supported shaft over a support, a pair of opposing pulleys secured to the shaft in such a way that they rotate together with said shaft, a pair of support cords, one end of which is secured to the suspended element while the other end is secured to the respective pulley, in which each of the pulleys includes a circular groove in which the respective cords can be wound in order to move the suspended element, and in which said shaft is connected by one end to an elastic element whose opposite end is secured to a friction disc. The use of this mechanism facilitates the movements initiated by the user to vertically move the suspended element, as said movements are counterweighted at any point of the movements.